Ice makers for producing and harvesting ice are known. Prior art ice makers typically use a conventional vapor compression refrigeration cycle to produce the ice on plates. An ice harvest cycle is then used to harvest the ice.
Some prior art ice makers use a water defrost harvest that produces a dry, sub-cooled ice fragment. Ice is formed on only one surface of the evaporator surface. The other ice side of the evaporator surface is used for application of the defrost water to remove the ice. This type of ice maker is advantageous for its dry, sub-cooled ice fragment, which is preferred by many customers.
Other prior art ice makers use a hot gas generation to harvest the ice from the evaporator surface. However, these ice makers tend to produce a wet ice due to the heat input from their hot gas harvest method, require more complex refrigeration systems and are not as simple to operate and maintain as desired. Oil management and compressor flooding are typical problems on equipment of this design. In such prior art systems, to maintain a stable refrigeration system when the ice making (refrigeration) load is removed during harvest, either multiple harvests would be required or the compressor would have to be stopped and restarted. In addition, larger suction accumulators and special oil management schemes would have to be used to handle the liquid refrigerant condensed during the harvest cycle. Large burn-off coils would also be required in the suction accumulator to boil off the liquid refrigerant to convert it a gas so it could be safely returned to the compressor. Furthermore, gaseous refrigerant generated by the evaporation of the liquid in the suction accumulator would create an additional load on the compressor and reduce the useful work, i.e., capacity, of the compressor in the ice making process. Although the liquid sub-cooling, resulting from the evaporation of the liquid, would offset some of the earlier compressor losses during the burn-off of the refrigerant, the additional liquid sub-cooling was not available during the entire cycle, making control of the refrigerant under all operating conditions more difficult. It is believed that compressor problems in previous systems were typically the result of the large quantities of refrigerant being rejected to the suction accumulator when the evaporator returned to the ice making mode following a harvest cycle.
The ice maker of the present invention has an integral ice making and ice harvest circuit and unique harvest gas generation system which combines the best features of the other ice makers to obtain a superior dryer product while eliminating oil management problems, compressor flooding, and complex operating systems.
The present invention produces ice on the evaporator plates in the conventional manner, and can use both sides of the evaporator plates. To harvest the ice, hot refrigerant gas is introduced to the evaporator, where it is condensed, raising the temperature of the plate and freeing the ice. The condensed refrigerant is then delivered to a harvest gas generator plate, which takes the condensed liquid refrigerant from the ice making plates and, by flowing make-up water which evaporates the liquid refrigerant while pre-cooling water for the next ice-making cycle. This is accomplished while maintaining a stable refrigeration system operation (with the compressor operating) even though the normal refrigeration load is removed, i.e., the ice making process is terminated.
The evaporation of the condensed liquid in the gas generator plate while pre-cooling incoming make-up water for the next ice making cycle converts the condensed liquid to useful work, rather than resulting in energy losses from the burn-off of large refrigerant quantities in the suction accumulator, as in conventional hot gas harvest systems. The gas generator circuit also eliminates the liquid handling and oil management problems of prior systems while using a standard, smaller suction accumulator with a built-in oil return system. Thus, external oil management systems are not required, resulting in a tremendous cost savings and a more efficient system. Even with the smaller physical size of the system, the capacity (ice production) is higher (approximately 70%) other than other ice makers with the same amount of evaporator surface.